Study of Efficacy and Safety in Premenopausal Women With Hormone Receptor Positive, HER2-negative Advanced Breast Cancer

Inclusion Criteria

• Key inclusion criteria: - Patients had advanced (locoregionally recurrent or metastatic) breast cancer not amenable to curative therapy - Patients were premenopausal or perimenopausal at the time of study entry - Patients who had received (neo) adjuvant therapy for breast cancer were eligible - Patients had a histologically and/or cytologically confirmed diagnosis of estrogen-receptor positive and/or progesterone receptor positive breast cancer - Patients had HER2-negative breast cancer - Patients must have either had measurable disease or If no measurable disease was present, then at least one predominantly lytic bone lesion - Patients had an Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1 - Patients had adequate bone marrow and organ function Key exclusion criteria: - Patients who had received a prior CDK4/6 inhibitor - Patients were postmenopausal - Patients who currently had inflammatory breast cancer at screening. - Patients who had received any prior hormonal anti-cancer therapy for advanced breast cancer, except for ≤ 14 days of tamoxifen or NSAI ± goserelin for advanced breast cancer prior to randomization. - Patients had a concurrent malignancy or malignancy within 3 years of randomization, with the exception of adequately treated basal cell skin carcinoma, squamous cell skin carcinoma, non-melanomatous skin cancer or curatively resected cervical cancer. - Patients with CNS metastases. - Patients had active cardiac disease or a history of cardiac dysfunction - Patients were currently using other antineoplastic agents - Patients were pregnant or nursing or physiologically capable of becoming pregnant and not using highly effective contraception.